Soft sensing of system parameters in membrane distillation

Abstract

Various examples of methods and systems are provided for soft sensing of system parameters in membrane distillation (MD). In one example, a system includes a MD module comprising a feed side and a permeate side separated by a membrane boundary layer; and processing circuitry configured to estimate feed solution temperatures and permeate solution temperatures of the MD module using monitored outlet temperatures of the feed side and the permeate side. In another example, a method includes monitoring outlet temperatures of a feed side and a permeate side of a MD module to determine a current feed outlet temperature and a current permeate outlet temperature; and determining a plurality of estimated temperature states of a membrane boundary layer separating the feed side and the permeate side of the MD module using the current feed outlet temperature and the current permeate outlet temperature.

The invention claimed is: 
     
       1. A system for water desalination, comprising:
 a membrane distillation (MD) module including a feed side and a permeate side separated by a membrane having a membrane boundary layer, wherein the feed side further comprises a feed inlet and feed outlet and wherein the permeate side further comprises a permeate inlet and permeate outlet: 
 temperature sensors configured to monitor feed solution temperatures at the feed outlet and permeate solution temperatures at the permeate outlet; and 
 processing circuitry configured to estimate, during steady- and unsteady-state operation, feed solution temperatures along the membrane boundary layer, on the feed side, and permeate solution temperatures along the membrane boundary layer, on the permeate side of the MD module using an Advection-Diffusion Equation (ADE), wherein the processing circuitry utilizes, as inputs, the monitored feed solution and permeate solution temperatures at the feed outlet and permeate outlet, respectively, 
 wherein the ADE includes a first part that describes the unsteady-state operation, a second part that describes a heat convection transfer between the feed side and the permeate side, and a third part that describes a heat conduction transfer between the feed side and the permeate side, and 
 wherein the processing circuitry is further configured to control operation of the MD module comprising maintaining, at a desired reference value, a difference between the feed solution temperatures along the membrane boundary layer, on the feed side, and the permeate solution temperatures along the membrane boundary layer, on the permeate side, based on the estimation. 
 
     
     
       2. The system of  claim 1 , wherein the processing circuitry is further configured to estimate a membrane mass transfer coefficient of the MD module. 
     
     
       3. The system of  claim 1 , wherein the feed solution temperatures and permeate solution temperatures include boundary temperatures along the membrane boundary layer. 
     
     
       4. The system of  claim 1 , wherein the Advection-Diffusion Equation (ADE) is a two-dimensional ADE model including dimensions of the membrane. 
     
     
       5. The system of  claim 4 , wherein the ADE model includes a plurality of grid points extending across the feed side and the permeate side of the MD module. 
     
     
       6. The system of  claim 5 , wherein the feed solution temperatures and permeate solution temperatures include temperatures corresponding to at least a portion of the plurality of grid points. 
     
     
       7. The system of  claim 1 , wherein the MD module is a counter current direct-contact MD module. 
     
     
       8. A method for water desalination, the method comprising:
 monitoring feed solution temperatures at a feed outlet and permeate solution temperatures at a permeate outlet of a membrane distillation (MD) module; 
 determining, during steady- and unsteady-state operation, a plurality of estimated temperature states along a membrane having a membrane boundary layer separating the feed side and the permeate side of the MD module using an Advection-Diffusion Equation (ADE), 
 wherein the ADE utilizes, as inputs, the feed solution temperature monitored at the feed outlet and the permeate solution temperature monitored at the permeate outlet, wherein the ADE includes a first part that describes the unsteady-state, a second part that describes a heat convection transfer between the feed side and the permeate side, and a third part that describes a heat conduction transfer between the feed side and the permeate side; and 
 controlling operation of the MD module comprising maintaining at a desired reference value, a difference between the feed solution temperatures along the membrane boundary layer, on the feed side, and the permeate solution temperatures along the membrane boundary layer, on the permeate side, based on the determining. 
 
     
     
       9. The method of  claim 8 , further comprising estimating a membrane mass transfer coefficient of the MD module. 
     
     
       10. The method of  claim 8 , further comprising adjusting characteristics of the feed solution or permeate solution based at least in part upon the feed solution temperature monitored at the feed outlet and the permeate solution temperature monitored at the permeate outlet. 
     
     
       11. The method of  claim 8 , wherein the estimated temperature states include temperatures corresponding to grid points extending across the feed side and the permeate side of the MD module. 
     
     
       12. The method of  claim 8 , wherein the ADE model is a two-dimensional ADE model including dimensions of the membrane. 
     
     
       13. A system for water desalination, comprising:
 a membrane distillation (MD) module including a feed side and a permeate side separated by a membrane having a membrane boundary layer; 
 temperature sensors configured to monitor feed solution temperatures at a feed outlet and permeate solution temperatures at a permeate outlet; and 
 processing circuitry configured to (1) apply an Advection-Diffusion Equation (ADE) model to estimate, during steady- and unsteady-state operation, feed solution temperatures and permeate solution temperatures along the membrane boundary layer, within the feed side and the permeate side, respectively, of the MD module using an Advection-Diffusion equation (ADE), wherein the feed solution temperatures monitored at the feed outlet and the permeate solution temperatures monitored at the permeate outlet are used as inputs to the ADE model, and (2) control operation of the MD module based at least in part upon the feed solution temperatures estimated within the feed side and permeate solution temperatures estimated within the permeate side, 
 wherein the ADE model includes a first part that describes the unsteady-state, a second part that describes a heat convection transfer between the feed side and the permeate side, and a third part that describes a heat conduction transfer between the feed side and the permeate side, and 
 wherein the processing circuitry is further configured to control operation of the MD module comprising maintaining, at a desired reference value, a difference between the feed solution temperatures along the membrane boundary layer, on the feed side, and the permeate solution temperatures along the membrane boundary layer, on the permeate side, based on the estimation. 
 
     
     
       14. The system of  claim 13 , wherein the processing circuitry is further configured to estimate a membrane mass transfer coefficient of the MD module. 
     
     
       15. The system of  claim 13 , wherein the feed solution temperatures and permeate solution temperatures include boundary temperatures along the membrane boundary layer. 
     
     
       16. The system of  claim 13 , wherein the estimated temperatures include temperatures corresponding to grid points extending across the feed side and the permeate side of the MD module.